The HK-55/fsk 420 and 55 inch rail is the kit I bought recently.
Yes, it has a Plug-it cord, it's a heavier cord than tools like the sanders use though, it will fit the sander, but the sander's cord won't fit the saw (there is a notch in the plug that prevents this).
Not sure about the blade speed, but I've not found it to be a problem, whatever it is. Yes, the spec as presented on the web site seems odd, especially compared to the battery version.
The retract mechanism on the FSK rail works smoothly and doesn't really slam anything back to the starting point. I don't know if there is a bumper though. I think the little sled that engages with the saw is plastic, the lever to release the saw is metal, and it doesn't have a bumper, but it doesn't seem to be a problem.
I was expecting to need a finer blade, but as Untidy Shop says, the standard blade produces a nice cut. I've not had any problems with tear-out on the hardwood ply I've been cutting with it.
It's a nice saw, I like it better each time I use it.